The present invention relates to dispersants for use in fuels and in engine oil lubricants, especially for reducing soot-induced viscosity increase in heavy duty diesel engines.
Heavy duty diesel vehicles may use exhaust gas recirculation (EGR) engines in efforts to reduce environmental emissions. Among the consequences of recirculating the exhaust gas through the engine are different soot structures and increased viscosity of the oil at lower soot levels, compared with engines without EGR. It is desirable that oil exhibit minimal viscosity increase, e.g., less than 12 mm2/sec (cSt) at a soot loading of 6%. A material that attenuates viscosity increase typically disperses soot up to high soot loading.
Dispersants have been used to improve the soot handling capabilities of lubricants and dispersants have also been reacted with various agents in order to improve their performance. U.S. Pat. No. 5,102,570, Migdal et al., Apr. 7, 1992, discloses a lubricating composition which has a major amount of oil and a minor amount of a dispersant prepared by coupling an alkenyl succinimide with an aldehyde and a hydroxyaromatic amine that can then be acylated.
U.S. Pat. No. 6,107,258, Esche et al., Aug. 22, 2000, discloses functionalized olefin copolymers that provide dispersancy properties, comprising acylated olefin copolymers containing a reactive carboxylic functionality reacted with a coupling compound which contains more than one amine, thiol and/or hydroxy functionality which is also reacted with a performance enhancing compound which contains only one functional group capable of reacting with the carboxylic functionality of the acylated olefin copolymer. See also the European Patent Application 909,805, Esche et al., filed Oct. 7, 1998, covering the same invention.
The present invention provides a polybutylene-based dispersant that is post-treated with an amine and an aldehyde, and optionally with a maleinated olefin copolymer. The present invention is distinguished from earlier dispersants by means of, among other things, the use of amines and aldehydes and optionally maleinated olefin copolymers in the post-treatment. The present materials typically exhibit superior performance in soot handling tests. Moreover, the synthesis of the present materials is based upon polybutylene dispersants which are typically significantly simpler and less costly than the synthesis of dispersants based on ethylene/propylene copolymers. In the preparation of polybutylene-based dispersants, the polymer preparation typically only requires a single catalyst, and extremely flammable hydrogen gas is not required as a chain terminator. The polymers in question have the advantage of providing olefin unsaturation and thus being suitable for further functionalization with or without a catalyst or solvent.
The present invention, therefore, solves the problem of providing a low cost dispersant having improved performance in soot handling tests, providing a good viscosity index and good soot dispersion and toleration properties, particularly in diesel engines, and especially in heavy duty diesel engines employing exhaust gas recirculation.